Centrifugal model tests on face failure of earth pressure balance shield induced by steady state seepage in saturated sandy silt ground

When tunnelling in a stratum with a high level of water (e.g., tunnelling below the river) by earth pressure balance shield, seepage due to the difference of hydraulic head between the ground and the shield's chamber can result in the failure of tunnel face. In order to investigate the failure of the tunnel face induced by the steady state seepage, a centrifuge model test device was developed and a series of the centrifugal model tests was performed. With the increase of the horizontal displacement of the tunnel face, it is found that the effective support pressure firstly decreases steeply to the limit effective support pressure and then increases gradually to a steady value. It is also found that the limit effective support pressure approximately increases linearly with the increase of the difference of hydraulic head between the ground and the chamber. Two available theoretical methods were compared with the measurement. In the limit state, a wedge-prism failure mechanism occurs in front of the tunnel face, and the failure zone has expanded to the ground surface. On the condition of a steady-state seepage, the pore pressure in the limit state /t urn gradually increases from the tunnel face to the far ground. The results of this paper may help to guarantee the face stability of the shield tunnels in a stratum with a high water level.